E67 Tach signal pinout

[HBHRaing]

Hello all. We have an E67 ECM that is being used with an 08 TBSS motor swap into a Jeep. The last issue we have is the tach signal. We are using the stock jeep cluster and PCM for the gauge, and a conversion box supplied by the manufacture of the swap kit. Our problem is the tach wire. Its been set to the White wire on connector X1, Pin 25. When we looked at the ECM, we found that it was set to serial data, instead of the crank signal that we needed. We set it to Crank, but I think that like the E38, The Tach output will now be on a different pin. What I need is the correct pin location. I have been searching around and have found that on the E38, it is C1, Pin 48. However on the E67, that pin in already in use. Any help would be great. Thanks.

[Taz]

Hello all. We have an E67 ECM that is being used with an 08 TBSS motor swap into a Jeep. The last issue we have is the tach signal. We are using the stock jeep cluster and PCM for the gauge, and a conversion box supplied by the manufacture of the swap kit. Our problem is the tach wire. Its been set to the White wire on connector X1, Pin 25. When we looked at the ECM, we found that it was set to serial data, instead of the crank signal that we needed. We set it to Crank, but I think that like the E38, The Tach output will now be on a different pin. What I need is the correct pin location. I have been searching around and have found that on the E38, it is C1, Pin 48. However on the E67, that pin in already in use. Any help would be great. Thanks.

C1 (Blue) pin 25 is where the Tach output will be - with an E67 ECM running a Trailblazer tune. The stock Tach setting in a Trailblazer is PWM - if memory serves. Changing this setting to "Crank" does not change the output pin of the ECM. When set to PWM or Crank the Tach output will be via the previously described pin.

Check your wiring. If everything checks out, your Tach setup may require a pull-up circuit to amplify the Tach signal sent from the ECM.


Regards,
Taz

[HBHRaing]

C1 (Blue) pin 25 is where the Tach output will be - with an E67 ECM running a Trailblazer tune. The stock Tach setting in a Trailblazer is PWM - if memory serves. Changing this setting to "Crank" does not change the output pin of the ECM. When set to PWM or Crank the Tach output will be via the previously described pin.

Check your wiring. If everything checks out, your Tach setup may require a pull-up circuit to amplify the Tach signal sent from the ECM.


Regards,
Taz

We have switched the setting away from serial which is what was set up when it arrived. However we have no signal at all, just voltage (near 12V). I can wire a pull up circuit on the system to see if that gives me anything. I have seen several different OHM values called for, do you know what value would be good to try? Thanks for the reply.

[Taz]

What Tach (Jeep IPC / Auto Meter / etc.) are you trying to use ?


Regards,
Taz

[HBHRaing]

Stock Jeep PCM (97 Wrangler), Stock Cluster. Between the GM Tach signal and the Jeep PCM is an emulator from Novak that takes the 2 Pulse/rev Signal from the GM tach wire, and converts it to a Jeep Cam/Crank signal. That signal is then converted in the Jeep PCM and sent to the cluster.

[Taz]

Yikes !! I have never worked with this combination before - so I don't have a known fix for you. When I encounter similar issues, I try to separate things into segments, and work through each segment, until I arrive at a known function.

In this case, I would suggest grabbing a Tach of known good function from your workbench, and wiring it up. It can be anywhere - under the hood / compartment floor / it doesn't need to be mounted. Once you get a usable signal to this test Tach, then proceed to connect to the conversion equipment, and diagnose from there.

Hopefully the answer turns out to be something simple.


Regards,
Taz

[HBHRaing]

Yikes !! I have never worked with this combination before - so I don't have a known fix for you. When I encounter similar issues, I try to separate things into segments, and work through each segment, until I arrive at a known function.

In this case, I would suggest grabbing a Tach of known good function from your workbench, and wiring it up. It can be anywhere - under the hood / compartment floor / it doesn't need to be mounted. Once you get a usable signal to this test Tach, then proceed to connect to the conversion equipment, and diagnose from there.

Hopefully the answer turns out to be something simple.


Regards,
Taz

I actually tied into a coil trigger and ran it through the conversion. Basically to simulate the tach signal from the gm computer. Obviously It's one pulse per 2 revolutions so the rate was wrong, but everything worked. So I know all I'm lacking is the gm pulse. I'll try a pull up circuit to see if that will produce the signal I need, but otherwise I'm stuck. Thanks for the help.

[Taz]

... have an E67 ECM that is being used with an 08 TBSS motor swap ... Our problem is the tach wire. Its been set to the White wire on connector X1, Pin 25 ... the ECM, we found that it was set to serial data, instead of the crank signal that we needed. We set it to Crank ...

Just reread your original post ... something is not right.

Can you post your tune ?

What tuning software are you using ?


Regards,
Taz

[HBHRaing]

We used EFI Live. I do not have the software here. A client opened it up for us. I know it was set for serial, we changed that selection. However I do not recall any other options being edited. I think there were only 2 or 3 fields that could be edited in the tacho section.

[Taz]

Read the tune from the ECM, and post it when you are able. A 2008 TBSS would have been set to PWM from the OEM. Apparently yours was not set this way - so either it has been previously altered, or is not actually a TBSS tune (despite what the VIN may indicate).

Also, the 2008 E67 Tach parameters include "Serial" if using HPT, or "Can Bus" if using EFILive.


Regards,
Taz

[HBHRaing]

Just confirmed. We have it set to crank, and the on/off cells set at 10. Which should be enough to at least get a signal. But I still have about 10.5V steady, both Key on and engine running.

[HBHRaing]

Read the tune from the ECM, and post it when you are able. A 2008 TBSS would have been set to PWM from the OEM. Apparently yours was not set this way - so either it has been previously altered, or is not actually a TBSS tune (despite what the VIN may indicate).

Also, the 2008 E67 Tach parameters include "Serial" if using HPT, or "Can Bus" if using EFILive.


Regards,
Taz

I'll try and get a copy of the tune. Long story short, a 4x4 shop did this conversion. They had issues with the wiring system and sub let the Jeep to us to fix. The company that sold the conversion is Novak. Basic motor, tranny, harness, PCM "kit". The ECM was tuned by them (or somone tuned it for them) before being shipped out. So yes, it's not a stock tune. I just talked to our tuner and he pulled up the calibration file. It's set to "crank" on/off both at 10. It says in the tune that if any other output is selected besides serial, the out put moves to pin 48. However I don't think thats true on the E67, but is true on the E38. Confused yet? We sure are.

[Taz]

You need to post the tune. All else is merely guess work. Tach output set to PWM or Crank, uses the same ECM pin per controller type (E38 or E67). If set to Can Bus, then the Tach output is communicated to the IPC over the GMLAN (Can Bus) network.

I'll check this thread again tomorrow if time permits.


Regards,
Taz

[efiharness]

on the e67 we use J1-25 tach out
J1-24 pull up, so just connect the 2 pins and go to the tach input. Steve

[GMPX]

Tach output set to PWM or Crank, uses the same ECM pin per controller type (E38 or E67).
I have not seen that to be the case.
In factory calibrations where the Tach is PWM or Crank the matching wiring diagrams shows J1-25 as the Tacho out, I'm with efiharness on this one.

[Taz]

I have not seen that to be the case.
In factory calibrations where the Tach is PWM or Crank the matching wiring diagrams shows J1-25 as the Tacho out, I'm with efiharness on this one.

Apparently my previous post (#13) only made sense to me. The original poster had wondered if the Tach output pin changed if the calibration setting was altered (i.e. from PWM to Crank). I had attempted to explain the the Tach output pin remains the same (whether using an E38 or E67 ECM) when the calibration is set to PWM or Crank.

In the case of an E38 - the Tach output remains on C1 (Black) pin 48.

In the case of an E67 - the Tach output remains on C1 (Blue) pin 25.

For corroboration of the E67 Tach output - take a look at schematics for a 2007 Trailblazer (set to PWM) and a 2007 CTS-V (set to Crank). Both of these use C1 pin 25.

Regarding Steve's comments about using C1 pin 24 as a pull-up circuit - I will take him at his word. I have never tried this - as in most applicable schematics this pin is listed as "Not used".


Regards,
Taz

[efiharness]

Pin C1-24 has a 2.4k pull up resistor built in so it makes a perfect place to do this (side by side to tach output). Steve

[GMPX]

I had attempted to explain the the Tach output pin remains the same (whether using an E38 or E67 ECM) when the calibration is set to PWM or Crank.
Sorry, I read that as both ECM's use the exact same pin, eg, both used C1, 48.

[Taz]

Sorry, I read that as both ECM's use the exact same pin, eg, both used C1, 48.

No worries ... I confuse myself sometimes !


Cheers,
Taz

[shoshorton]

Greetings - I've been following and learning a ton over the past year with my build. Still a complete newbie but wanted to confirm Steve's (efiharness) recommendation regarding the e67 C1-24 for pull up. Just dropped a connector in the slot and connected it to C1-25 going to my tach. Works perfectly. I did have to adjust G1202 & G1203 from 15 to 7 to get it dialed in but assuming that varies based on application.

Thanks for all the great information you guys provide.

Steve